Snowfall level detector

ABSTRACT

Apparatus for detecting the occurrence of an amount of snowfall, or of drifting snow, above a predetermined level and providing a signal at a remote location. A light source, a light sensor, and a plurality of apertured baffle members are mounted on a base plate. The light source is arranged to project a beam of light through the apertures in the baffle members at a predetermined distance above the base plate for detection by the sensor. Upon interruption of the light beam by accumulated snow a signal is produced to activate an alarm or the like to thereby indicate that a predetermined level of snowfall or drifted snow has occurred.

United States Patent [1 1 0 Ver Sluis 111 3,801,779 1 Apr. 2, 1974SNOWFALL LEVEL DETECTOR [76] Inventor: David G. Ver Sluis, 8897Vergennes, S.E., Ada, Mich. 49301 [22] Filed: May 3, 1972 [21] Appl.No.: 249,826

Primary Examiner-James W. Lawrence Assistant Examiner-D. C. NelmsAttorney, Agent, or Firm--Price, Heneveld, Huizenga & Cooper 57 ABSTRACTApparatus for detecting the occurrence of an amount of snowfall, or ofdrifting snow, above a predetermined level and providing a signal at aremote location. A light source, a light sensor, and a plurality ofapertured baffle members are mounted on a base plate. The light sourceis arranged to project a beam of light through the apertures in thebaffle members at a predetermineddistance above the base plate fordetection by the sensor. Upon interruption of the light beam byaccumulated snow a signal-is produced to activate an alarm or the liketo thereby indicate that a predetermined level of snowfall or driftedsnow has occurred,

14 Claims, 3 Drawing Figures PATENTEDAPR 2 I314 v $801,779

1 F K f in i' 36 74 A 8 M L A u 82 43 2e 28 I I4 36 FIG. 2

SENSOR SOURCE ls z T 66 POWER 74a SUPPLY 64 I 68 so 88 86 E ALARM Ii: FIG 3 T 2 1 7e BACKGROUND OF THE INVENTION In the past, a number ofdifferent types of snowfall detection devices have been conceived todetect the presence or the amount and level of snowfall. One such priorart device, illustrated in U.S. Pat. No. 3,141,330, discloses aprecipitation monitoring device utilizing photocells to monitor thereflectivity of the snowfall to indicate the density of the fall. Theactual amount of snowfall is detected by the snow falling on a tuningfork and thereby changing its fundamental frequency. Another method ofdetecting accumulated precipitation is illustrated in US. Pat. 2,717,957wherein a heater element melts the snow and the resultant liquid levelis measured.

Detection of snowfall is useful for many reasons. A primary applicationto which most individuals are familiar is for the daily reports issuedby the United States Government National Weather Service. Another groupof individuals who are extremely concernedwith the amount of snowfallare those charged with responsibility for snow removal from streets andhighways, as well as the many service companies who make a business ofremoving snow from driveways, sidewalks, parking lots, and the like on acontract basis. Business places subscribing to such services usuallycontract with a snow removal service company to maintain their premisesin essen-tially snow-free condition. One ofthe requirementsgenerally isthat the walks, drives and parking lots be cleared prior to the timethat employees or other individuals arrive at the business place. Thisrequires that the snow removal operator constantly watch the level ofaccumulated snow so that when it accumulates above a predeterminednegligible level he can promptly get his equipment into operation. Ifsnowfall occurs during the night, as is often the case, the operatormust awake and get up several times during the night to check the levelof the snow so that excessive amounts are not allowed to accumulate; Asis well known, snow plowing is often an all-night or evenaround-the-clock job during the several winter months in many parts ofthe country, when shownfalls are steady and sizeable, particularlyduringlarge storms. This is a'severe physical drain on the humanoperators, who need all'the rest they can get during such times. Forthis reason it is particularly desirable for such per sons to havesnowfall detection equipment which will with complete reliabilitygenerate a signal or other indication after a predetermined amount ofsnow. has accumulated. In addition, the typical winds associated withwinter weather can often cause drifting and blowing of snow which haspreviously fallen, causing it to drift into the cleared areas andrequiring plowing even though no new snowfall has occurred during thatperiod.

The above-described prior art devices are rather complex in theiroperation and are very expensive, particularly the first such device,being well out of the economic reach of the average small business snowplow operator. In addition, these devices have no facility for detectingdrifting snow but rather only measure the amount falling directlydownwardly. Furthermore, devices of the type which melt the snow andmeasure the liquid equivalent are subject to freezing and, as aconsequence, unreliable operation. It is therefore desirable to providea snowfall detection apparatus which is rela- 2 tively inexpensive,simple in operation, extremely reliable, and which in addition candetect drifted snow.

SUMMARY OF THE INVENTION The present invention relates to a snowfalldetection device and more particularly to a detection device which isrelatively simple in construction and is uniquely adapted to provide asignal when the fallen snow has reached a predetermined level. Theapparatus is adapted to detect not only the level of directprecipitation but is also equipped to detect and provide a signal whenan amount of drifting snow exceeds a predetermined level.

The snowfall detection apparatus of the present invention includes alight source, a light sensor and a plurality of apertured baffle membersmounted on a base plate. The light source is arranged to project a beamof light through the apertures in the baffle members at a predetermineddistance above the level of the base plate for detection by the sensor;Snow accumulating on the base plate and held by the baffles about theareas of the apertures interrupts the light beam, triggering a signal toproduce an audible alarm or other indication to the operator.

It is therefore a primary object of the present invention to provide anapparatus for the detection of snowfall above a predetermined level.

It is another object ofthe present. invention to provide a snowfalldetection apparatus which is simple in construction, relativelyinexpensive to manufacture and which operates with complete reliability.

It is an additional object of the present invention to BRIEF DESCRIPTIONOF THE DRAWINGS FIG. 1 is a top plan view of the snow-detectingapparatus of the invention; 1

FIG. 2 is a side view, partially in section, of the apparatus of FIG. 1;and

FIG. 3 is a schematic block diagram illustrating an electrical system tobe utilized in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2of the drawings the snowfall apparatus of the present invention will bedescribed in detail. The apparatus is illustrated generally by thenumeral 10 and is divided into three basic sections: thesnow accumulatorsection 20, a light beam transmitter 30, and a light beam receiver 40cooperatively arranged on an elongated rectangular mounting or baseplate 12.

The accumulator section 20 is located in the approximate center of themounting plate 12 and includes a plurality of diagonally positionedelongated barrier members which may be angle stock of L-shaped crosssection. As shown in FIG. 1 a first elongated barrier member 22 extendsdiagonally across the mounting plate 12 from the lower left hand portionto the upper right hand portion. The barrier member 22 has an opening 23(FIG. 2) therein at its central portion and in alignment with theapproximate centerline of the mounting base 12. A second barrier member24 having an opening 25 therein is positioned in abutment against (orvery close to) the first barrier member'and extends perpendicularthereto, toward the lower right of the base plate 12. The opening25 issimilarly positioned in alignment with the approximate centerline of thebase plate 12. A third barrier member 26 similar in construction to thesecondbarrier member 24 is also positioned in end abutment or closelyadjacent, and perpendicular to, the first barrier member24 and extendstoward the upper left of the base plate. An opening 27 provided in thethird barrier member is also positioned in substantial alignment withthe approximate centerline of the base plate.

The presence and to a certain extent the relative position of thebarrier members with respect to each other is an important feature ofthe present invention. It should be noted that barrier members 24 and 26extend perpendicular to barrier member 24 in opposite directions and donot intersect or lie in alignment with each other at their point ofintersection with barrier member 22, but instead'have their axes spaceda slight distance apart. This particular feature further contributes tothe .of condensation as will be more fully described herein utility ofthe invention with respect to the detection of drifting snow as will bemore fully described hereinafter.

The barrier members 22, 24 and 26 may be fixed to the base plate 12 inany desired manner, as by suitable screws or like fastening means 28passing through the lower leg of each of the L-shaped barrier membersandthreadably relieved in the base'plate. A section of insulating material29 may be positioned below the barrier members on the plate 12, in anarea generally about the apertures-23, 25 and 27. The insulatingmaterial preferably is a fibrous material such as polymeric carpetingand serve to prevent the snow falling thereon from melting upon contactwith the base member 12. This would occur if, for example, the apparatuswere exposed to sunlight thereby warming the base material such that itmight still contain an amount of residual heat to melt the new fallensnow. I

Thetransmitter 30 is adapted to project a light beam B along theelongated axis of the base plate 12, through the openings 23,25 and 27,to the sensor 40. Transmitter 30 includes a light source, which may be aconventional bulb 31 mounted in a conventional socket 32. The socket isfixed in an L-shapedbracket 33. The bracket is provided with anelongated slot 34 at its extending leg portion. A plurality ofadjustment washers 35 are positioned below the bracket 33 on thebasepanel 12. A screw and lock washer 36 passing through the elongated slotin the bracket through the washers 35 secures the bracket to the basemember 12. The screw may be loosened and the bracket moved along theelongated slot and washers may be removed or added to adjust theposition of the light source both horizontally and vertically.

The entire transmitter assembly 30 is encased in a weather proof housing37 of bakelite or the like and fixed to the mounting plate 12. Anopening 38 covered by a window 39 is provided at one end of the housingfor the light beam B to project through. The window 39 is of atransparent material such as glass or clear plastic and is fixed at theinside of the housing. A lens 52 fixed between the window and the lightsource 31 focuses the light beam emitted from the light source.

' The receiver 40 is positioned at the opposite side of the base plate12 to detect the presence (or absence) of the light beam emitted fromthe transmitter. The sensor is enclosed in a weather-tight housing 41,similar in construction to the housing previously discussed inconnection with the transmitter 30. An opening 42 is provided at one endthereof having a suitable window 43 therein to admit the projected lightbeam B. A light beam sensor 44 such as a photocell, is positioned withinthe housing and arranged to detect the presence of the light beam B. Aheating element 82, as for example a nichrome wire coil, may bepositioned between the window 43 and the sensor 44 to prevent theformation after. Upon interruption of the light beam B by the snowblocking the apertures 23, 25 or 27 in the barrier members, a signal isprovided to produce an audible alarm or other indication at a remotelocation to thereby indicate to the operator that the level of snow hasreached or exceeded the predetermined level.

A mounting bracket or flange 50 (FIG. 2) having a downwardly extendingtubular mounting post is preferably provided on the lower surface of thebase plate 12 for conveniently mounting the entire assembly. Theassembly is preferably mounted in a clear exposed area such thatprecipitation may fall thereon without obstruction by trees, buildingsand the like.

The electrical circuit utilized in the practice of this invention may beof a basically conventional nature and includes a relay or otherswitching means normally held in a first switching mode in response toimpingement of the light beam on the sensor. Upon interruption of thelight beam by the level of snow accumulating above the transmission pathof the light beam, the interruption causes the relay to switch to asecond conduction mode thereby actuating an alarm. A basic block diagramof one such switching circuit is shown in FIG. 3. Since such circuitsare generally well known to those skilled in the-art, a detaileddiscussion and description thereof is not believed necessary. Briefly,the circuit includes the aforementioned transmitter or light source 31and receiver on sensing element 44, each connected to a suitable power.source 62. In the preferred embodiment, low voltage DC power issupplied to the transmitter and receiver circuits through suitableelectrical wiring 64 and 66. The sensor 44, as previously mentioned, isa photocell or similar lightdetecting device which responds to thepresence or absence of the projected light beam B. A relay 68 having acoil 70 and a pair of contacts 72 has its coil 70 connected to thesensor 44 by means of wire 74. In its preferred embodiment, the coil isenergized through suitable conventional circuitry associated with thesensor to hold the contacts 72 of the relay in an open position. Analarm means 76 which may be either of a visual or audible type is alsoconnected to power supply 62 by means of wires 78 and 80 through thecontacts 72 of the relay 68. I

When quantities of snow arecam'ed by the wind, this blowing snow canoccasionally cause momentary inter ruption of the light beam,particularly if the sensor has been set for a very low threshold, i.e.,for extreme sensitivity, thereby causing the alarm to oscillate betweenan OH and on position. Since it is desirable to sense only a completeinterruption of the light beam as by fallen or drifted snowsubstantially blocking the apertures in the accumulator 20, acurrent-limiting circuit may, if desired, be provided to decrease thesensitivity of the apparatus. In one embodiment of the invention, thisis accomplished by reducing the light output of the transmitter byintroducing a current-limiting means such as a resistor in series withline 64 connecting the power supply 62 to the light source 31. Toaccomplish this, a current-limiting switch 84 is shown connected in line64 and may be of conventional construction wellknown to those skilled inthe art. One such switch of this nature need only include a latchingrelay (not specifically shown) operable in response to closing of thecontacts 72 of relay 68, i.e., closing of the contacts 72 may be used toprovide a signal through line 86 to the current-limiting means 84 toconnect a current-limiting component in series with light source 31 toreduce the power supplied to, and thereby reduce the output intensityof, the light source. Suitable holding circuit 14 may also be includedin the current-limiting means 84 connected via line 88 to the powersupply to maintain the current-limiting means in seriesafter initialswitching. Suitable manual switching means (not shown) may also beprovided to selectively switch the currentlimiting means 84 into or outof circuit with the line 64 and the source 31. Other arrangements fordecreasing the sensitivity of the apparatus will be readily apparent tothose skilled in the art.

It should be pointed out that the circuitry associated with the sensor44 may (and preferably does) include means such as a manually variableresistance for adjusting the light-responsive characteristics of thesensor 44, to allow the user to vary the threshold at which the alarmwill be triggered, to satisfy particular requirements. That is someusers may want extreme sensitivity and low threshold, so that they areforwarned at the earliest possible time that snow is in the air, whileothers may wish to have the alarm operate only under very heavy or densesnow conditions. In this respect, it should also be pointed out that itis certainly within the concept of the invention to change the relativeheight of the apertures in the barriers and of the light beam withrespect to the level of the base plate, to vary the height at whichcollected snow about the apertures causes a triggering of the alarm.This can be accomplished by merely providing spacing means of differentheights for positioning upon the base plate under the barriers and thesensor on receiver housings, to raise the level of the lattercomponents; of course, it would also be entirely feasible to mount suchcomponents independently of the platform or base and provide amechanical or other position-adjustment mechanism therebetween.

To prevent condensation from forming on the window 43 associated withthe receiver section 40, a heating element 82 may be positioned adjacentthe window 43 within the housing. The heating element 82 may simplycomprise a small length or coil of Nichrome or like toaster wire; toproduce a small amount of heat near the window 43 and thereby preventthe formation of frost, ice or like condensation on the windows.

OPERATION In use, the apparatus is placed in an. open, exposed area byfixing the mounting flange to a suitable mounting post, pole, or thelike. The light source is energized and adjusted to project the beam oflight B through the apertures 23, 25, and 27 in the barrier members sothat the light impinges on the photosensor 44. The alarm re mains in anoff position so long as the beam continues to impinge on the photosensor44 because the circuitry associated therewith keeps the relay coilenergized, holding the relay contacts 72 in an open condition. Whensnow, sleet, hail or other precipitation begins to fall, it accumulateson the insulating material 29 within the accumulator area 20. Theaccumulator area 20 is preferably divided into a plurality ofaccumulating zones or sections labeled C, D, E, and F, each defining anarea of intersection between two angularly disposed parts of the barriermembers. As snowfall or other precipitation continues to gradually pileup in all or any one of the accumulatingvzones, it eventually covers atleast one of the apertures 23, 25, or 27 in the barrier members. Whenany one of the apertures is covered, the light beam is interrupted,degenerizing the coil 70 of relay 68 thereby closing the contacts 72.This in turn applies power from the power supply through wire 80,contacts 72, and wire 78 to thereby actuate the alarm 76.

The barrier members are positioned in a somewhat cruciform pattern suchthat the openings therein are positioned angularly with respect to theaxis of the light beam. Through extensive experimentation, it has beendetermined that the light to moderate breezes and wind usuallyassociated with a light, direct, snowfall (as contrasted to a blizzard)will not adversely affect the sensitivity of the instrument. Theparticular arrangement of the barrier members prevents the snow fromcovering the openings until a generally even level of snow is depositedin at least one of the sections C, D, E, or F, of the accumulator as thelight breezes, regardless of their prevailing direction, will bedirected along the barriers and either dissipated or blow the snowthrough the opening. If, for example, the breeze is directed from thetop of the drawing as illustrated in FIG. 1, that portion of thebarriers 22 and 26 defining area C will prevent the snow from blowingout of this area. Similarly, a breeze blowing from the oppositedirection, i.e., from the bottom of FIG. 1', will cause the snow toaccumulate in area E. Actually, the wind may be directed from virtuallyany orientation about the apparatus and at least one of the definedareas C, D, E, or F will remain unaffected by the wind. The wind howeverwill blow the snow through the openings keeping them clear until snowhas accumulated in at least one area to interrupt the light beam.

The barrier members also serve to detect drifting snow upon theoccurance of extremely strong winds which cause the snow to drift intoareas previously cleared, even in the absence of new snowfall. Thebarrier members serve to duplicate or simulate the environmental areasabout which snow tends to drift. As the strong winds carrying driftingsnow tend to move about and direct their force at the surfaces of theaccu-. mulator area 20, snow will accumulate and pile up or driftadjacent the barrier members. While much of the accumulator may berelatively snow-free, the drifted snow against at least one of thebarriers will eventually cover at least one of the openings,interrupting the light beam to thereby activate the alarm.

It has also been determined through extensive observation that theseartificially-created miniscule snow drifts are representative of thedrifting snow in an environmental area subjected to the same winds.

7. lt'may therefore be seen that the present invention provides arelatively simple apparatus for detecting the accumulation of snow undergiven environmental conditions. The apparatus is extremely simple inconstruction and in its operation thereby rendering it well within theeconomic reach of the independent snow removal operator. It iscompletely reliable, thereby eliminating this necessity of the operatorto constantly monitor changing weather conditions as he can rest assuredthat upon the occurence of snow fall or drifting snow abovepredetermined levels that an alarm or other indication will be given.

While a preferred embodiment of the invention has been illustrated anddescribed it will be recognized that other embodiments and modificationsof this invention incorporating the teachings hereof may readily be madein the light of this disclosure. Therefore all modifications employingthe principles of this invention are considered as included in theappended claims unless' these claims by their language expressly stateotherwise.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A snowfall level detector-comprising: a transmitter adapted toproject a beam of electromagnetic radiation along a path at apredetermined level above a reference plane; a receiver positioned alongsaid predetermined path and adapted to detect said beam ofelectromagnetic radiation, said receiver having means associatedtherewith to provide a signal upon interruption of said beam; andupstanding wall means for catching and trapping falling and driftingsnow in the space generally between said transmitter and said receiverand in the path of said beam, said means including at least one memberhaving an opening therein at said predetermined level to allow passageof said beam therethrough whereby the accumulation of snow above saidpredetermined level interrupts said light beam thereby causing saidsensor to provide said signal.

2. The apparatus as defined in claim 1, wherein said transmitter andsaid receiver are a light beam projector and'alight-responsiveelectrical device, respectively.

3. The apparatus as defined in claim 1, wherein said receiver and saidtransmitter are positioned on a generally flat planar mounting plate,said mounting plate providing a reference plane for said beam.

4. The apparatus as defined in claim 3, wherein said mounting plate hasa heat-insulating carpet means on at least portions thereof.

5. The apparatus as defined in claim 3 and further including: housingmeans for generally enclosing said transmitter and said receiver; windowmeans in said housing for allowing the passage of said light beam fromsaid transmitter to said receiver; and heating means for at leastpartially preventing the formation of condensation over said windowmeans.

6. The apparatus as defined in claim 5, wherein said heating means ispositioned in said housing adjacent said window.

7. The apparatus as defined in claim 3, wherein said wall means comprisea plurality of upwardly extending barrier members arranged on saidmounting plate in a generally cruciform pattern with respect to saidpath.

8. The apparatus as defined in claim 7, wherein said barrier meansdefine an opening about the point of intersection of said members, atthe intersecting portion of said cruciform pattern. Y

9. The apparatus as defined in claim 2, and further including means forvarying the intensity of said light beam to thereby vary the sensitivityof said detector.

10. The apparatus as defined in claim 9, wherein said light beamprojector is adapted for connection to a source of power and said meansfor varying the intensity of said beam is selectively connectable inseries circuit between said projector and said source.

1 1. An apparatus for detecting snowfall above a predetermined levelcomprising: a base plate; means for transmitting a beam ofelectromagnetic radiation at a predetermined level above a generallyparallel to said base plate; means for detecting said beam ofelectromagnetic radiation; alarm means connected to said de tectingmeans, said alarm means responsive to interruption of said beam;accumulating means positioned between said transmitting means and saiddetecting means, said accumulating means including barrier membershaving open spaces therein to permit the passage of said beamtherethrough from said transmitting means to said sensing means; saidbarrier means cooperatively forming wind deflection means to entrapwind-driven snow to thereby simulate snow drifting environmentalconditions wherein said drifting snow obscures said apertures therebyinterrupting said beam and actuating said alarm.

12. A method of detecting the level of snowfall above a predeterminedlevel comprising: transmitting a beam of electromagnetic radiation at apredetermined level above a reference place; detecting said beam ofelectromagnetic energy; using upstanding wall means to trap falling andwind-driven snow and to accumulate the same in an area through whichsaid beam of electromagnetic radiation is transmitted; and sensing theinterruption of said beam to thereby indicate that said falling snow hasexceeded a predetermined level.

13. A snowfall level detector comprising: means defining a snowfallaccumulator; a light beam transmitter means positioned to transmit abeam of light across said accumulator; a receiver positioned to detectsaid beam of light and to provide a signal upon interruption of saidbeam; and signal responsive means connected to said receiver to providean indication upon the interruption of said light beam said meansdefining said accumulator comprising a plurality of vertical upstandingbaffle members having apertures therein positioned between saidtransmitter and said receiver, said light beam passing through saidapertures from said transmitter to said receiver; said baffle membersdefining a plurality of mutually independent areas in which snow mayaccumulate, each of said areas including a portion therein through whichsaid beam is projected, whereby accumulation of snow is any one of saidplurality of areas interrupts said light beam thereby activating saidalarm.

in said mutually independent areas.

1. A snowfall level detector comprising: a transmitter adapted toproject a beam of electromagnetic radiation along a path at apredetermined level above a reference plane; a receiver positioned alongsaid predetermined path and adapted to detect said beam ofelectromagnetic radiation, said receiver having means associatedtherewith to provide a signal upon interruption of said beam; andupstanding wall means for catching and trapping falling and driftingsnow in the space generally between said transmitter and said receiverand in the path of said beam, said means including at least one memberhaving an opening therein at said predetermined level to allow passageof said beam therethrough whereby the accumulation of snow above saidpredetermined level interrupts said light beam thereby causing saidsensor to provide said signal.
 2. The apparatus as defined in claim 1,wherein said transmitter and said receiver are a light beam projectorand a light-responsive electrical device, respectively.
 3. The apparatusas defined in claim 1, wherein said receiver and said transmitter arepositioned on a generally flat planar mounting plate, said mountingplate providing a reference plane for said beam.
 4. The apparatus asdefined in claim 3, wherein said mounting plate has a heat-insulatingcarpet means on at least portions thereof.
 5. The apparatus as definedin claim 3 and further including: housing means for generally enclosingsaid transmitter and said receiver; window means in said housing forallowing the passage of said light beam from said transmitter to saidreceiver; and heating means for at least partially preventing theformation of condensation over said window means.
 6. The apparatus asdefined in claim 5, wherein said heating means is positioned in saidhousing adjacent said window.
 7. The apparatus as defined in claim 3,wherein said wall means comprise a plurality of upwardly extendingbarrier members arranged on said mounting plate in a generally cruciformpattern with respect to said path.
 8. The apparatus as defined in claim7, wherein said barrier means define an opening about the point ofintersection of said members, at the intersecting portion of saidcruciform pattern.
 9. The apparatus as defined in claim 2, and furtherincluding means for varying the intensity of said light beam to therebyvary the sensitivity of said detector.
 10. The apparatus as defined inclaim 9, wherein said light beam projector is adapted for connection toa source of power and said means for varying the intensity of said beamis selectively connectable in series circuit between said projector andsaid source.
 11. An apparatus for detecting snowfall above apredetermined level comprising: a base plate; means for transmitting abeam of electromagnetic radiation at a predetermined level above agenerally parallel to said base plate; means for detecting said beam ofelectromagnetic radiation; alarm means connected to said detectingmeans, said alarm means responsive to interruption of said beam;accumulating means positioned between said transmitting means and saiddetecting means, said accumulating means including barrier membershaving open spaces therein to permit the passage of said beamtherethrough from said transmitting means to said sensing means; saidbarrier means cooperatively forming wind deflection means to entrapwind-driven snow to thereby simulate snow drifting environmentalconditions wherein said drifting snow obscures said apertures therebyinterrupting said beam and actuating said alarm.
 12. A method ofdetecting the level of snowfall above a predetermined level comprising:transmitting a beam of electromagnetic radiation at a predeterminedlevel above a reference place; detecting said beam of electromagneticenergy; using upstanding wall means to trap falling and wind-driven snowand to accumulate the same in an area through which said beam ofelectromagnetic radiation is transmitted; and sensing the interruptionof said beam to thereby indicate that said falling snow has exceeded apredetermined level.
 13. A snowfall level detector comprising: meansdefining a snowfall accumulator; a light beam transmitter meanspositioned to transmit a beam of light across said accumulator; areceiver positioned to detect said beam of light and to provide a signalupon interruption of said beam; and signal responsive means connected tosaid receiver to provide an indication upon the interruption of saidlight beam said means defining said accumulator comprising a pluralityof vertical upstanding baffle members having apertures thereinpositioned between said transmitter and said receiver, said light beampassing through said apertures from said transmitter to said receiver;said baffle members defining a plurality of mutually independent areasin which snow may accumulate, each of said areas including a portiontherein through which said beam is projected, whereby accumulation ofsnow is any one of said plurality of areas interrupts said lIght beamthereby activating said alarm.
 14. The apparatus as defined in claim 13,including a carpet of heat-insulating material disposed as a floor insaid mutually independent areas.